Spin-transfer torque magnetic random-access memory (STT-MRAM) is a type of solid state, non-volatile memory that uses tunneling magnetoresistance (TMR) to store information. An MRAM device comprises an electrically connected array of magnetoresistive memory elements, referred to as magnetic tunnel junctions (MTJs). As is known in the art, a basic structure of a magnetic tunnel junction includes two thin ferromagnetic layers separated by a thin insulating layer through which electrons can tunnel. The spin-transfer torque (STT) phenomenon is realized in an MTJ structure, wherein one ferromagnetic layer (referred to as “magnetic free layer”) has a non-fixed magnetization, and the other ferromagnetic layer (referred to as a “magnetic pinned layer”, or “reference layer”) has a “fixed” magnetization.
An MTJ stores information by switching the magnetization state of the magnetic free layer. When the magnetization direction of the magnetic free layer is parallel to the magnetization direction of the reference layer, the MTJ is in a “low resistance” state. Conversely, when the magnetization direction of the free layer is antiparallel to the magnetization direction of the reference layer, the MTJ is in a “high resistance” state. The TMR of an MTJ determines the difference in resistance between the high and low resistance states. In general, the TMR of an MTJ is defined as (RAP−RP)/RP where RP and RAP are the resistance of the MTJ for parallel and anti-parallel alignment of the ferromagnetic layers, respectively. A relatively high difference between the high and low resistance states facilitates read operations in the MRAM. The difference in resistance of these two states of the MTJ is used to indicate a logical ‘1’ or ‘0’, thereby storing a bit of information. The tunneling current is typically higher when the magnetic moments of the two ferromagnetic layers are parallel and lower when the magnetic moments of the two ferromagnetic layers are anti-parallel.
When fabricating MRAM devices, the MTJ structures are typically encapsulated in a layer of insulating/dielectric material, and conductive contacts are formed in the encapsulating layer of insulating/dielectric material to make electrical connections to and between the MTJ structures in an MRAM array. Conventional processes and materials that are used for encapsulating the MTJ structures and patterning the encapsulating material to form contact openings to the MTJ structures, can cause a signification degradation in the electrical and/or magnetic performance of the MTJ structures.